Rheostat



Aug. 3, 1948. D IN 2,446,417

RHEOSTAT I Filed Feb. 1, 1946 INVENTOR.

DONALD 'F, HASTINGS Patented Aug. 3, 1948 UNITED STATES PATENT OFFICE RHEOSTAT Donald Francis Hastings, Fair Lawn, N. .L, as-

signor to Hardwick, Hindle, Inc., Newark, N. J.

Application February 1, 1946, Serial No. 644,877

7 Claims.

This invention relates to the design of a rheostat of the type that is suitable for mounting on panel boards or equivalent supports. Where rheostats of the type to be hereinafter described are used with high operating temperatures it is the usual practice to insert an electrical insulator which will stand up under these temperatures between the drive shaft and the contact members. In many cases this insulator also serves to transmit torque from the shaft to the movable contact member.

It is the object of my present invention to simplify the construction and to prevent as much as possible any lost motion between the shaft and the movable contact member because any lost motion or play between the insulator and the contact arm is magnified at the point where the arm contacts with the brush track of the resistance wire, this magnification being dependent upon the ratio between the distance from the center of the shaft to the point of play and the distance from the center of the shaft to the point of brush contact. I have found it :desirable to put this point of play as far away from the axis of the shaft as possible as it is one of the objects of my invention to eliminate as much as possible this lost motion.

Another object of my invention is to provide a construction which is easy to assemble and disassemble and hence reduces the cost of manufacture and maintenance. My improved type of construction will be understood from the annexed drawing, wherein,

Figure l is a plan view of the contact end of the rheostat with the contact member in one position of operation.

Figure 2 is a part sectional and part elevational View taken on the line 22 of Figure 1.

Figures 1 and 2 are full-size views of an operative structure.

Figure 3 is a view on an enlarged scale looking at the end of the drive shaft removed from the support and without the switch contact member.

Figure 4 is a view on an enlarged scale of the movable contact member as shown in Figure l but from the reverse side.

Figure 5 is a full-size view of a stationary contact member of the rheostat.

In the different views, I is a support of suitable insulating material preferably of the ceramic type. The support I has a circular central portion 2 which is connected to a vertical sector 3. The support I carries a cylindrically formed resistance unit 4 which may be fastened to the support I in any satisfactory manner, many of which are known in the trade. The unit 4 is made up of an arcuately shaped core with a resistance winding 5 thereon one end of the resistance wire being connected to a terminal 32 the wire being imbedded in enamel in the usual manner, a brush track 5 being left at the outer edge of the unit. The support I carries a bearing 6 preferably of suitable metal. The inner end of the bearing has a polygonally shaped head 1 to non-rotatably hold the bearing in position. The outer end of the bearing has threads 8 to receive a lock nut 9 that also holds a plate ID in position. Seated on the central portion 2 of the support I is a fixed contact member 11 having a plurality of lugs I2 bent downwardly over the edge of the part 2 and with a positioning lug l'3 therein to engage a recess in the vpart 3 of the support I. All of the foregoing has been briefly described as these parts form no part of my present improvement which resides in the parts to be now described.

The bearing 6 carries a shaft I4 which extends all the way through the bearing and through the support I. The brush track end of the shaft I4 is of a smaller diameter than the rest of the shaft and on this smaller diameter is fastened a suitable member I5 having a suitable lug I6 to engage a cooperating part IT on the portion 3 of the support I. Also mounted on this reducedend of the-shaft I4 is a sleeve I8 which is preferably made of extruded ceramic material. I prefer to use an extruded part rather than a moulded part for I have found it to be more accurate hence lost motion of this part is reduced to a minimum. The sleeve I8 is drivingly held to the shaft I4 by a cap I9 that is fastened as by spot welding or riveting to the shaft. The cap is so formed that it fits over the outer surface of the sleeve I8 which surface has a square cross section. Mounted on the sleeve between the stop member and the cap I9 is a cup shaped member v2i) having a square hole through the bottom to slidably fit satisfactorily on the sleeve I8. Within the cup is carried a spring 2| the purpose of which will be later described. Also slidably positioned on the sleeve I8 is a spring contact member having a part 22 formed between spaced arms 23 and 24 that pass around the cup 28. The arms 23 and 24 terminate in an integral contact portion 25. Opposite the contact 25 the arms 23 and 24 are rebent into a circular formed portion 26 that has a square hole 21 to snugly fit the square surface of the sleeve I8 to thereby receive a driving connection from the shaft I4.

Extending from the ring portion 26 is a lip 28 which serves to prevent accidental deformation of the part 22 and contact portion 25.

While the spring contact member may be mounted on the sleeve l8 before the cap 19 is fastened in place, I have shown an alternative method of assembling the spring on the sleeve. This alternative method is obtained by forming a slot 29 as indicated by the broken line in Figure 4 thus allowing the ring portion 26 to be passed back of the stop lug l6.

After the shaft with its parts have been assembled as described the shaft is passed through the clearance hole in the stationary contact member H and through the bearing 8 into the position shown in Figure 2. The operating end of the shaft I4 is provided with a groove within which 1 is positioned a washer 3i] and a split lock ring 3 I which holds the shaft M in the position shown in Figure 2. In this position the ring portion 26 is held by spring 21 in resilient contact engagement with the fixed contact member H, while the rebent resilient arms 23 and 24 hold contact 25 in resilient engagement with the brush track 5. It will be noted that in this assembled position the contact members are positioned a considerable distance away from the stop member i which is free to engage its cooperative stop I! in the support I. It will also be noted in this position that the cap 49 is positioned substantially Wholly within the cup 2!! thereby ore-determining to some extent the amount of tension exerted by the spring 2|.

Having thus described my invention, what I claim is:

1. In a rheostat having a circularly formed resistance unit With a brush track and mounted on a support of suitable insulating material, the support non-rotatably carrying a bearing for an operating shaft which extends through the bear ing and support; means for carrying a contact member on one end of said shaft, said means including a sleeve of suitable insulating material fitting over the shaft at the brush track end, the sleeve having an external polygonally shaped surface, a cap fastened to the extremity of the shaft and having a shape to drivingly fit around the external surface of the sleeve, a cup slidably fitting over said sleeve back of the cap and having an internal diameter to receive the cap, a spring carried within the cup between its bottom and the cap, a spring contact member having a part slidably fitting the external surface of the sleeve and another part free of the sleeve and. the cup and extending into contact with the brush track, a stop carried by the shaft for engaging a cooperative part of said support, a stationary contact member positioned around said sleeve out of driving engagement therewith but adapted to rest on said support and means cooperative between the shaft and its bearing to hold the shaft so the contact members are in continuous operative position. v

2. A rheostat as set forth in claim 1 further characterized in that the shaft end carrying the sleeve is of reduced diameter forming a shoulder for said stop while the sleeve has a, bore to fit on the reduced shaft end, the external surface of the sleeve forming a square while the cap has inwardly turned flanges to drivingly fit the square.

3. A rheostat as set forth in claim 1 further characterized in that the spring contact member comprises a ring portion having a polygonally shaped hole to snugly fit around the external surface of the sleeve, the ring portion having two spaced arms extending upwardly and then out around the cup into a union which forms a contact to engage the brush track.

4. A rheostat as set forth in claim 1 further characterized in that the spring contact member comprises a contact portion for engaging the track with a pair of arms curving outwardly around and free from the cup one on each side and then being joined to a ring-like part that extends under the arms and has a hole therein to drivingly fit the external surface of the sleeve, the ring having a clip extending upwardl and over said contact portion.

5. A rheostat as set forth in claim 1 further characterized in that the external surface of the sleeve is square in cross section and the cap has flanges to fit around this surface within the cup While that part of the spring contact member which is carried on the sleeve has a square'hole to fit the square surface of the sleeve, and the said hole on one side may have a recess to clear a part of said stop for purpose of assembly.

6. In a rheostat 0f the type described having a resistance unit with a brush track thereon, a support therefor and an operating shaft; means for carrying on the shaft a contact member having two spaced parts, said means including a sleeve of suitable insulating material carried on one end of the shaft, the sleeve having its external surface polygonal in shape, a driving connection between the shaft end and the sleeve in the form of a cap fastened to the shaft and embracing the external surface of the sleeve, a cup of suitable insulating material slidably fitting the sleeve but non-rotatable thereon, a spring within the cup and having one end engaging the said cap, a contact member in two spaced parts, one part having a hole to snugly fit over the sleeve while the other part has two spaced curved arms passing oppositely around the cup and joined to form a contact to engage the brush track, a stationary contact member carried by the support and means for positioning the shaft so said spring resiliently holds the movable contact member in engagement with the stationary contact member.

'7. A rheostat as set forth in claim 6 further characterized in that when the parts are in fully assembled operative position the cap is located substantially within the cup and has inwardly turned flanges which engage the outer surface parts of the sleeve.

DONALD FRANCIS HASTINGS.

REFERENCES CITED The following references are of file of this patent:

UNITED STATES PATENTS record inthe Number 

